1. Field of the Invention
The present invention relates to a semiconductor element comprising a semiconductor junction composed of silicon-based films, and a method of forming silicon-based films.
2. Related Background Art
When a crystal phase is contained in an i-type semiconductor layer substantially functioning as an light-absorbing layer in a photovoltaic element having a pin junction, a photodegradation phenomenon, which results from a Staebler-Wronski effect and poses a problem in the case of an amorphous semiconductor, is advantageously suppressed. Accordingly, it is effective that the i-type semiconductor layer contains a crystal phase. Further, a high-mobility TFT is required for a high-definition and high-luminance liquid crystal panel. However, a silicon TFT in a crystal phase has a higher mobility than an amorphous silicon TFT by two orders or more, so that even if TFT characteristics are substantially improved and the TFT has a significantly reduced gate width, a current value required for circuit operations is ensured and a reduced pixel pitch is obtained compared to amorphous silicon TFTs. Consequently, it becomes relatively easy to reduce the size of the apparatus and increase the definition thereof.
Under these circumstances, various attempts have been made for silicon-based thin films containing a crystal phase.
A high-frequency plasma CVD process is one of the excellent methods for enabling silicon-based thin films to be mass-produced partly because this process allows silicon-based thin films larger in area to be formed at low temperature and improves process throughput. Examples of application of silicon-based thin films to products include solar cells and color liquid crystal TFTs, but to popularize these silicon-based films, costs must be further reduced and the performance thereof increased. Thus, establishment of techniques for the high-frequency plasma CVD process is an important technical object.
As a crystal silicon-based thin film layer using a (220) face as a growth face, Japanese Patent Application Laid-Open No. 11-310495 discloses a silicon-based thin film characterized in that the (220) face has a diffraction intensity of 30% or more to the total diffraction intensity.
Further, as an example of an element with a semiconductor layer having a pin junction in which an i-type semiconductor layer is composed of microcrystalline silicon, Japanese Patent Application Laid-Open No. 11-233803 discloses a photovoltaic element wherein the orientation property of a crystal in the i-type semiconductor layer changes in a depth direction.
As described previously, the silicon-based thin films exhibit excellent characteristics. However, the former application describes a silicon-based thin film in which the crystal is preferentially oriented along the (220) face, but does not refer to the distribution of the orientation property. Further, the latter application does not refer to a silicon-based thin film in which the crystal is preferentially oriented along the (220) face.